To assess the effects of starvation on Synechogobius hasta intestinal function and morphology, fish were starved for 3, 7 and 14 days, followed by the measurement of histological, physiological and transcriptional responses in the intestine. Intestinal length was significantly lower in S. hasta starved for 7 and 14 days (p < 0.05). Intestinal amylase activity was significantly decreased upon fasting (p < 0.05), whereas a lower level of intestinal lipase activity was not observed until the end of the trial. After 7-day starvation, the intestine of starved S. hasta exhibited exfoliated villus cells, increased vacuoles and widened cell interstices. Regarding the expression of lipid metabolismassociated genes, poststarvation transcript levels of lipoprotein lipase, carnitine palmitoyltransferase 1 a and fatty acid transport protein 1 significantly increased with longer food deprivation periods (p < 0.05). Meanwhile, downregulation of stearoyl-CoA desaturase 1 was observed in the intestine upon starvation (p < 0.05). In summary, prolonged starvation (>14 days) not only disrupted the intestinal structure, which may further weaken digestive potential, but also attenuated intestinal lipid deposition by diminishing lipid biosynthesis, as well as upregulating lipolysis and fatty acid transport. Therefore, our findings provide preliminary data for further characterization of metabolic traits in starved S. hasta, which may have important implications for determining the appropriate starvation time applied in fasting/re-feeding regimes, as well as the sustainable development of S. hasta and other fish.

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Fish in natural and cultivated environments can be challenged by starvation. However, inducing starvation in a controlled manner cannot only reduce feed consumption but also reduces aquatic eutrophication and even improves farmed fish quality. This study investigated the effects of starvation on the muscular function, morphology, and regulatory signaling in javelin goby (Synechogobius hasta) by evaluating the biochemical, histological, antioxidant, and transcriptional changes in the musculature of S. hasta subjected to 3, 7, and 14 days fasting. The muscle glycogen and triglyceride levels in S. hasta were gradually reduced under starvation, reaching their lowest at the end of the trial ( P < 0.05 ). The levels of glutathione and superoxide dismutase were significantly elevated after 3–7 days of starvation ( P < 0.05 ), but later returned to the level of the control group. The muscle of starved S. hasta developed structural abnormalities in some areas after 7 days of food deprivation, and more vacuolation and more atrophic myofibers were observed in 14-day fasted fish. The transcript levels of stearoyl-CoA desaturase 1 (scd1), the key gene involved in the biosynthesis of monounsaturated fatty acids, were markedly lower in the groups starved for 7 or more days ( P < 0.05 ). However, the relative expressions of genes associated with lipolysis were decreased in the fasting experiment ( P < 0 .05). Similar declines in the transcriptional response to starvation were found in muscle fatp1 and ppar γ abundance ( P < 0.05 ). Furthermore, the de novo transcriptome of muscle tissue from the control, 3-day and 14-day starved S. hasta generated 79,255 unigenes. The numbers of differentially expressed genes (DEGs) identified by pairwise comparisons among three groups were 3276, 7354, and 542, respectively. The enrichment analysis revealed that the DEGs were primarily involved in metabolism-related pathways, including ribosome, TCA pathway, and pyruvate metabolism. Moreover, the qRT-PCR results of 12 DEGs validated the expression trends observed in the RNA-seq data. Taken together, these findings demonstrated the specific phenotypical and molecular responses of muscular function and morphology in starved S. hasta, which may offer preliminary reference data for optimizing operational strategies incorporating fasting/refeeding cycles in aquaculture.